The invention relates to an assembly for purifying toxic gases from production processes by thermal conversion in a reactor chamber and to the subsequent treatment of the reaction products with a sorbent in a washing device in order to bind water-soluble reaction products and to elute solid reaction products.
Toxic gases of this type accumulate in large quantities, for example, in the production of semiconductor circuits and cannot be disposed in an untreated form in the environment due to their toxicity. Examples of such toxic gases are HF, SiH2Cl2, SiCl4, NH3, C2F6, PH3, BCl3, NF3, etc.
It is well known that most of these waste gases from semiconductor processes or even from other different chemical processes can usually be rendered harmless by means of oxidation or thermal conversion. Usually, the thermal conversion is carried out in a flame, which is supplied with natural gas or hydrogen and air or oxygen. For this purpose, it is not necessary to supply additional reactants, with the exception of additional oxygen or air where appropriate. The thermally treated reaction products are completely harmless and are present either in gaseous or solid form or are water-soluble. The gaseous reaction products, such as water vapor or CO2 can be disposed in the environment without further subsequent treatment.
It should be understood that a number of combustion processes and reactor chambers have already been developed and used in practice for thermal conversion. Thus in the [European Patent specification] EP 0 346 803 B1, an assembly for purifying waste gases has been disclosed, which assembly comprises a reactor chamber in which there is arranged, at the bottom, a burner, which is operated on the one hand with combustible gases such as hydrogen and oxygen and/or air or natural gas and air and to which on the other hand the waste gas to be purified is supplied. The reaction product arising during combustion contains both solid components, and water-soluble reaction products.
In order to be able to completely eliminate these reaction products from the exhaust gas, the reaction products arising during combustion are brought into contact with a sorbent, for example water, immediately after combustion. This is carried out by arranging, above the burner flame, a spraying device for the water, which is sprayed against the ascending gas flow of the reaction products. The spraying device can be designed in such a way that the sorbent sprayed out is not sprayed into the flame (EP 0 702 771 B1). Alternatively, a splash guard device (cone or spherical caps or the like) is arranged above the burner flame and the spraying device is arranged above this splash guard device, as shown in EP 0 346 803 B1.
The aim here is that the water-soluble reaction products are dissolved from the burner exhaust gas and that the solid components (e.g., SiO2 as a reaction product of silane) are eluted from the reactor chamber. In addition, DE 196 00 873 A1 or even WO 03/085321 A1 provide for the reactor chamber to be delimited upwardly by a spray guard device and radially by means of a cylindrical wall and for the entire assembly to be encased by an external wall. Here, the solid reaction products are rinsed with the sorbent downwards along the inner face of the external wall, thus outside of the combustion chamber, and near the burner arranged at the bottom [text cut off] Here the disadvantage, in particular, is that the combustion must be carried out at relatively high temperatures and that the structural elements of the combustion chamber are thus also exposed to high temperatures or alternating thermal stress loads, thereby wearing out comparatively rapidly. Another disadvantage is that reaction products from the upwardly burning flame can get deposited in or on the burner. The consequence is a constant degradation of the effectiveness and the necessity for frequent cleaning procedures.
The latter disadvantage was eliminated to a large extent by arranging the burner nozzle at the top in the combustion chamber, as indicated in EP 0 803 042 B1 with the result that the flame burns downwardly. Deposits of solid reaction products on the burner were thus substantially reduced, thus achieving a clearly improved service life. However, the problem of the high temperature load of the reactor still persisted. The result is considerable servicing expenses.
In other waste gas purification methods, the operation involves the use of an upwardly burning flame and subsequent catalytic waste gas treatment (EP 0 736 322 B1). However, it has been shown that a concluding treatment with a sorbent is meaningful and necessary.